Control system for furnaces



Patented Jan'- 22, 1946 UNITED sr 'rEs' PATENT OFFICE Carl H. Diclie, Dayton,- Ohio, asslgnor to The Master Electric Company, a corporation of Ohio Original application January 21, 1941, Serial No.

Divided and this application December 23, 1942, Serial No. 489,970

8 Claims.

This invention relates to improvements in con-' trol system for furnaces, and more particularly for furnaces adapted to alternatively burn two types of fuel. The instant application. is a division' of my co-pen'ding application Serial Number 375,143, filed January 21, 1941 (Patent 2,335,- I

263,.November 30, 1943) An object of this invention is to provide an arrangement for improving the year-roundoperation of furnaces.

Another object of this invention is to provide an improved controlling system for furnaces adapted to burn two types of fuel, such as coal' and gas.

Still another object of this invention is to provide an economical, eflicient, automatic and reliable control system for furnaces adapted to burn solid and gaseous fuel. I

A further object of this invention is tocontrol a furnace burning both solid or gaseous fuel in accordance with the will of the operator, by a single automatic temperature-responsive unit.

A still further object of this invention is the vantages of the invention will appear from the subioined detailed description of a, preferred embodiment thereof, illustrated in the accompanying drawing, in which the single figure is a circuit diagram of a control system in accordance with the present invention, wherein the furnace damper and a gas valveare controlled by a single room thermostat.

The form of invention illustrated in the figure, illustrates a control system for a furnace generally indicated at 2, adapted to be supplied with both solid and fluid fuel. The furnace 2 will have suitable fire-controlling dampers for use in connection with the solid fuel, such as the draft damper 4, as well as means such as the pipe for the entrance of the fluid fuel, which ma be; for example, gas. The furnace is primarily under the control of a suitable temperature-responsive device such as the usual room thermostat 2, which.

may be of the two-way or three-wire type. The

' latter is adapted to control the opening and closing of the dampers by suitable means such as the damper motor generally indicated at I0, and the magnetically operated, normallyclosed gasvalve I2, depending upon the position of the season switch I4, in a manner to be described in more detail hereinafter. The system may also include a suitable basement switch It for use in connection with the firing of the solidfuel.

As shown in the figure, theroom thermostat 0 is in its off' position, the season switch 14 is in the position for solid fuel control, the basement switch. It is in its normal position, the gas valve I2 is in its closed position, while draft damper 4 of furnace 2 is closed. If, now, the temperature of the space to be heated lowers sufllciently' to move the room thermostat 8 to the "on position, a circuit will be established beginning with one end of the transformer secondary winding 22, conductor 200, damper motor I8, conductors I06, 202; and 203, contact arm 30 and contact 38 of basement switch I6, conductor 204, arm 206, and closed contact 200, 2I0, of thermostat 8, conductor 2I2, contact arm 50,, and contact of season switch I4, conductor 2| 4, brush 92 commutator segment 94, brush 96, and conductor 2I0, to the other side of winding 22. The-damper motor 18 is accordingly energized to raise the damper 4 from the closed to the open position, the circuit for the damper motor; being transferred from brush 92 to brush I02 by the commutator 94. This results from the fact that as the damper motor 18 is rotated, it also rotates the commutator 94 to such an extent that the brush 92 will meet the cut-out section I00, ,thus breaking the motor circuit through that brush; however, before the commutator has moved this far, the brush I02 will leave the cut-out section I04 and engage the commutator 94, thus main taining the motor circuit through conductor I06, brush I02, commutator 04, to brush 06, independently of the brush 92. The motor will continue to rotate until the commutator has moved approximately or until the brush I02 is inv the cut-out'section I00, at which time the energizing circuit for the motor 10 will be entirely interrupted. However, at this point, a suitable crank IIII driven by the motor 10 and interconnected with the draft damper 4' by suitable means such as chain II 2 willhave moved the damper to the open position, to increase the combustion in'the furnace in accordance with the call of the room thermostat.

If, now, the room thermostat 0 is satisfied and being run on solid fuel.

tablished for the damper motor I8 to return the damper 4 to its closed position. This circuit may be traced from one end of the transformer secondary winding 22, conductor 200, motor 18, conductors I06, 202, and 203, contact arm 36 and contact 38 of basement switch I6, conductor 204, arm 206, and closed contacts 208 and 220 of thermostat 8, conductor 222, brush I22, commutator 94, brush 96, and conductor 2 I8 to the other side of winding 22. After the damper motor has started to rotate its control circuit will again be transferred to brush I02, and the damper 4 will be moved to its closed position. It will be seen that after the damper motor and commutators have moved slightly in a direction to close the damper, the brush I22 will fall within the cut-out section of the commutator, but again just before this happens, the brush. I02 will have contacted the commutator 94, maintaining the energizing circuit for the motor 18 as previously traced when the motor was raising the draft damper. Also, similarly, when the motor has rotated approximately 180 and the draft damper is now closed, the brush I02 will fall within the cut-out portion I04 so that the motor will stop and the damper remain closed.

If, at any time, as during the spring and early fall, it is desired to operate the furnace on gas, the season switch I 4, as seen in the drawing, is thrown to the left. If the room-thermostat 8 is now moved to the on" position, a closed circuit entirely independent of the source of power I3 will be established, while the circuits to the damper motor are interrupted. This closed circuit may be traced, for example, from arm 206 of room thermostat 8, conductor 204, contact 38 andcontact arm 36 of basement switch I6, conductors 203 and 232, thermo-couple 224, conductor 226 energizing winding I40 for gas valve I2, conductor 230, contact I32, and contact arm 58 of season switch I4, conductor 2| 2, and closed contacts 2I0 and 208 to the arm 206 of the thermostat. Power for energizing the coil I40 to raise the valve I2 is, in this case, derived from the thermo-couple 224'heated by the pilot I31. When the room thermostat is satisfied and its contacts ,are moved to off position, the closed circuit energizing th'e valve winding I40 will be opened, and the valve will accordingly close.

The system illustrated in the drawing is, as will have been noted, also provided with a suitable basement switch which may shunt the fon contact of the room thermostat 8 to open the draft damper 4 for firing when th'e furnace is If the basement switch I6 is moved to its open position, a damperraising circuit for the damper motor will be established from one end of the transformer secondary winding 22, conductor 200, damper motor 18, conductors I06, 202, and 203,'contact arm 36 and contact I44 of basement switch I6, conductor 234, contact arm 28 and contact 30 of the switch I4, conductors 236 and 2I4, brush 92, commutator 94, brush 06, and conductor 2I8 to the other end of winding 22. Again, after the motor has rotated a certain amount, contro1 of its circuit will be transferred from brush 92 to brush I02 to complete the raising operation. If the season switch is in position for gas firing, movement of the basement switch to open position will be ineffectual to open the draft damper. This follows from the fact that when the basement switch is in its open position, the circuit for the damper motor must be traced through contact 30 of the season switch 14, but this contact is engaged only when the season switch is in the solid fuel firing position.

Various changes in the above-described system will occur to those skilled in this art and are conteniplated as forming part of the present invention. For example, additional safety limit switches may be added to the system where deemed desirable. While the system has been illustrated as operated upon low voltage, by a proper choice of equivalent parts the system may be used on any ordinary voltage. Additionally, various units forming the system have been diagrammatically indicated by way of illustration, and it will-be obvious that well-known equivalent parts can be used in place of those shown. While no signal lamp has been illustrated as associated with the room thermostat, due to the fact that the ordinary thermo-metal will not provide enough power to both energize the valve controlling solenoid and a signal lamp, it is to be understood that another source of power other than the thermal couple might be used in this system, in which case the addition of a signal light might readily be included.

While, for the sake of simplicity, the damper motor has been illustrated as operating only a draft damper, it is to be understood that in accordance with usual practices, the damper motor may also operate a correlated checkdamper.

It has been found that the system illustrated and forming part of the present invention is unusually well adapted to control furnaces burning solid and gaseous fuels, since, in the fall and spring months a desirable level of heat is difficult to obtain with solid fuel alone, whereas gas is ideally suitable for heating at this time. Accordingly, it is contemplated that during the cold winter months the furnace will run on solid fuel,-

while during the fall and spring months the season switch will be thrown so that the furnace will run upon gas. However, it is clear that the invention in its broader aspects is not limited to thereto except as may be required by the following claims.

I claim:

1. Controlling system for a furnace adapted to burn both solid and gaseous fuel, said furnace having at least one controlling damper movable between fire-retarding and fire-accelerating positions, and a gas supply, the combination of a main .source of power, a damper motor for moving said damper from one of said positions to the other, a normally closed gas valve for controlling said gas supply, an actuating winding for opening said gas valve, a room thermostat movable between two contacts, adapted to engage one at a predetermined temperature and the other at a predetermined lower temperature, a double-pole double-throw season switch, means for connecting said damper motor to said source of power, in one position of said season switch, to move said damper motor to the fire-accelerating position when said room thermostat engages one conbetween fire-retarding and tire-accelerating positions and a gas supply, including an exterior source of power, electrically energizable means for controlling said damper associated with said exterior source of power, a self-contained source of power, electrically energiaable means for controlling said gas supply associated therewith, a thermostatically operated switch, and means for optionally interconnecting said thermostatically operated switch in series with either'the exsource of power.

3. A furnace control system havingdual optionally selective control circuits, including a first source of power, a damper motor actuated thereby, a second source of power, an electro-magneti- 1 cally operated gas valve actuated thereby, a single thermostatic switch and means for interconnecting said thermostatic switch to either said first or.

second source of power, the construction and arrangement being such that, at will, one ot a pinrality of control circuits may be established, one

means for shunting the one contact of said thermostat through said season switch in its one position by movement of said basement'switch to its other position, whereby movement of said season switch to its other position interrupts said shunt circuit.

5. A condition control system having dual optionally selective control circuits, each including an individual source of power and a device to be energized thereby, an energization control element responsive to changes in the condition to be controlled, means for placing in a selected circuit the condition responsive element thereby controlling the energization of the selected cirterior source of power or the self-contained from the first source of power through the thermostatic switch to the damper motor and the other from the second source of power through the thermostatic switch to the electro-magneticall operated gas valve,

4. Controlling system for a furnace adapted to .burn both solid and gaseous fuel,'said furnace having at least one controlling damper movable between fire-retarding and fire-accelerating positions, and a gas supply, the combination of amain source of power, a, damper motor for moving said damper from one of said positions to the other, a normally closed gas valve for controlling said gas supply, an actuating winding for opening said gas valve. a room thermostat movable between two contacts, adaptedto engagepne at a predetermined temperature and the other at a predetermined lower temperature, a double-pole double-throw season switch, means for connecting said damper motor to said source of power in one position ofsaid season switch to move said damper motorto the fire-accelerating position when said room thermostat engages one contact and to the fire-retarding position when said room thermostat engages the other contact, a secondary source of power, means for connecting said gas valve winding to said -sec ondary source of power in the other position ,of said season switch when said room thermostat engages said one contact, a single-pole double? throw basement switch having a "normal" posicult, and manually operable means in one of said control circuits for shunting the condition responsive element permitting manual energization of such circuit,

6. For a furnace wherein two um'elated fuels may be selectively used, a control system including two separate control circuits, one for each type oi fuel, an independent source of power for each circuit, regulating means in each circuit for controlling the rate of fuel combustion, a temperature responsive instrument, and means for making the temperature responsive instrument a part of either circuit, the construction andarrangement beingsuch that the temperature responsive instrument will control the regulating means of either circuit when made a part of such circuit.

Z. A control system for a furnace wherein both solid and gaseous fuels are burned, said 'fumace having at least one controlling damper movable between fire-retarding and fire-accelerating positions and'a gas supply, including an exterior source of power, electrically venergizable means for controlling said damper associated with said exterior sourceof power, a self-contained source of power, electrically energizable means for controlling said gas supply associated therewith, a thermostatically operated switch, and means for optionally interconnecting said thermostatically operated switch in series with either the exterior source of power and the damper controlling means or with the self-contained source of power, and electrical means for controlling the gas suply. p 8. A control system for a furnace wherein both solid and gaseous fuels are burned, said furnace having at least one controlling damper movable between fire-retarding and fire-accelerating positions and a gas supply, including an exterior source of power, electrically energizable means for controlling said damper associated with said exterior source of power, a self-contained source of power produced by heat generatedby said gaseous fuel, electrically energizable means for controlling'said gas supply associated with said tion through which said motor is connected to said source of power by said thermostat, andself-contained source of power, a thermostatically operated switch, and means for optionally interconnectina said thermostatically operated switch in series with either the exterior source of power or the self-contained source of power.

CARL H. mm. 

